Polyolefins, such as polyethylene and polypropylene, have become a preferred material for formed parts used in a variety of assembled products due to its balance of properties, ease of fabrication due to their thermoplastic nature, relatively low cost and polyolefin formulation technology which allows tailoring of their properties for certain uses. Polyolefins are used in a wide variety of industries such as automotive, furniture, electronics, toys, appliances and the like. The drawback with the use of polyolefins in assemblies of different materials is that polyolefins have low polarity on their surfaces which means that the coatings and adhesives preferred for use in industry based on polyisocyanate functional resins (polyurethanes) do not easily bond to polyolefins. In order to bond such materials to polyolefins, the polyolefin surface needs to be modified to facilitate bonding. It is well known to modify the surface of polyolefin parts to enhance adhesion to adhesives with polar groups. This is achieved by flame treatment, corona discharge treatment, etching physically or with chemicals or through the use of primers. Common primers used with polyolefins utilize chlorinated polymers or compounds, such as chlorinated polyolefins dissolved in non-polar solvents, Ryntz “Coating Adhesion to Low Surface Energy Substrates” Progress in Organic Coatings 25 (1994) pp 73-83. These methods require high capital investments, significant production floor space or present environmental concerns.
Recently acrylic based adhesive systems have been developed which bond well to low surface energy polymers such as polyolefins, see for example Skoultchi, U.S. Pat. Nos. 5,106,928; 5,143,884; 5,286,821; 5,310,835 and 5,376,746; Zharov et al., U.S. Pat. Nos. 5,539,070; 5,690,780 and 5,691,065; Pocius U.S. Pat. Nos. 5,616,796; 5,621,143; 5,681,910; 5,686,544; 5,718,977 and 5,795,657; and Sonnenschein et al. U.S. Pat. Nos. 6,806,330; 6,730,759; 6,706,831; 6,713,578; 6,713,579 and 6,710,145 (all incorporated herein by reference). These systems bond well to polyolefins and have been utilized commercially. In a commercial environment it is most efficient to cure these systems using ultraviolet light sources. The use of these systems are not as inexpensive as commercial epoxy resin and polyisocyanate functional group containing (polyurethane) systems. Thus many users of polyolefins based parts would prefer to use commercial polyisocyanate functional adhesive systems.
There have been attempts to develop other primer systems for polyolefin substrates, see Nakata et al. U.S. Pat. No. 6,348,123 and Iida JP, 2003213055A. It does not appear that these systems have achieved commercial success.
Components or parts prepared from polyolefins are often manufactured by component suppliers that sell and ship the components and parts to original equipment manufacturer that assemble components into sub-assemblies and final assemblies. Often the original equipment manufacturer requires that the part be assembly ready when received. This means that the surface of the polyolefin parts need to be modified by the component manufacturer in its plant and then shipped to the original equipment manufacturer. Thus it is important that the surface modification process allow for modification in a plant remote in time and place from the ultimate assembly plant. This requires that the surface once modified retain its ability to bond to common coatings or adhesives having polar functional groups when the parts are shipped to a different location for assembly.
What is needed is systems that facilitate the bonding of polar adhesive systems to polyolefins substrate surfaces. What is further needed is a system that facilitates modification of the surface in one location and the surface retains its ability to adhere to adhesives containing polar groups in another location at a time remote from the time of application.